The invention may be used, in particular, in high-tension circuit-breakers of the type in which a resistor or a varistor is inserted in parallel with the terminals of the arcing contacts for a relatively short period of time on circuit-breaker opening or on circuit-breaker closing.
Contact apparatus for such insertion is described in French Patent Application No. 91 06159, filed in the name of the Applicant. FIG. 1 of the present specification reproduces FIG. 1 of the above-mentioned document. FIG. 1 shows a circuit-breaker interrupting chamber comprising a gastight ceramic casing 1 delimiting a volume 2 filled with a gas under pressure and having good dielectric properties. The casing, which is closed at its top by a metal end plate 3, contains a fixed assembly comprising a first metal tube 6 constituting the fixed main contact, a second metal tube 7 constituting the fixed arcing contact, and contact fingers 31 connected to one end 20 of a varistor made up of a stack of disks 18 disposed in an insulating cylinder 19. The ends 31A of the arms 31 are made of an alloy that is resistant to the effects of electric arcing. The second end of the varistor, together with the fixed permanent contacts and the fixed arcing contacts are electrically connected via arms 5 to a first current terminal 4 of the circuit-breaker.
The moving assembly of the circuit-breaker comprises a cylinder 9 mechanically connected to a drive rod (not shown) and electrically connected to a second current terminal (not shown). A part 11 is fixed to the cylinder 9 and serves as a support for the fingers 12 constituting the moving permanent contact, for the fingers 14 constituting the moving arcing contact and disposed at the end of a tube 13, and for a blast nozzle 17. A cap 10 protects the fingers 12 from corona discharge. Holes 15 are provided in the part 11 to enable the blast gas to pass therethrough. The varistor is inserted in parallel with the arcing contacts on circuit-breaker opening by means of an inertia contact 43 in the form of a rod which is slidably mounted in a guide block 30 fixed to the cylinder 9, and which is provided with a cavity 32 in which the first end of a spring 34 surrounding the rod 43 bears, the other end of the spring abutting against a damping block 40 fixed to the end of the rod.
When the circuit-breaker opens, by means of the moving equipment being displaced, the rod 43 because of its inertia, remains stationary for a few instants against the pressure of the spring which is compressed. This enables the varistor to be inserted after the arcing contacts have moved apart, the varistor being inserted for the length of time required to attenuate any voltage surges. When the spring is fully compressed, the rod 43 is driven by the motion of the cylinder 9 and it moves away from the contact 31.
These dispositions also enable the varistor to be inserted on circuit-breaker closing, before the arcing contacts come together, by means of an appropriate choice of contact lengths.
The dielectric profile of the above-described apparatus is not suitable for very high tension equipment.